Technical Abstract:
A majority of state USDA-NRCS agencies, including Pennsylvania's, selected a Phosphorus (P) Index to assess P loss potential as part of their nutrient management 590 standard. As P continues to become an integral component of nutrient management plan development, there needs to be an ongoing Index assessment of how recommended manure management practices, nutrient applications, soil conservation practices, and land use changes are impacting the potential for P loss. Using the Pennsylvania P Index, P loss potential was determined over a 5-year period for 24 fields in a 39.5 ha central Pennsylvania agricultural watershed. The relative impact of manure management, land use, soil conservation practices, soil testing intervals, and actual soil test P levels on the P Index values will be presented. It will be shown that the assigned risk of P loss for fields in the watershed is very sensitive to land management practices, particularly manure application rate, which are under the farmer's control. Additionally, monitored water quality data over the 5-year period will be discussed in relation to modifications of farming practices and changes to P loss potential.